1. Field of the Invention
The present invention relates to a filtration apparatus for filtering an analytical sample including suspended matter as pretreatment of the sample and for supplying the filtrate to an analyzing apparatus.
2. Description of the Related Art
A filtration apparatus is used to adjust a sample for analysis and, in particular, a slurry sample including suspended matter. FIG. 7 shows an example of a general filtration apparatus. This filtration apparatus includes a filtration device 30 having, inside itself, a space 34 which serves as a filtration chamber for filtering a sample. A flat filtration filter 32 partitioning the space 34 into two is provided at a center of the space 34 in the filtration device 30. A pipe 36 for introducing the sample is connected to one end of the filtration device 30 and a pipe 38 for discharging filtrate is connected to the other end. The pipes 36 and 38 communicate with each other through the space 34 in the filtration device 30 and the filter 32 is disposed to be perpendicular to a flowing direction of fluid between the pipe 36 and the pipe 38.
In such a filtration apparatus, the filtration filter 32 is clogged with suspended matter in the sample and a flow rate of the filtrate passing through the filtration filter 32 reduces with the passage of time since the starting of the filtration, and therefore, cleaning for unsticking the suspended matter accumulating on a surface of the filtration filter 32 needs to be carried out periodically. In this case, a method of cleaning is backward cleaning for introducing a cleaning solution or a cleaning gas from the pipe 38 into the filtration device 30 with the introduction of the sample from the pipe 36 stopped, unsticking the suspended matter stuck on the filtration filter 32, and discharging the suspended matter through the pipe 36.
As the filtration apparatus, there is an apparatus using a cylindrical disc filter besides the apparatus using the flat filtration filter. In such a filtration apparatus, it is necessary to carry out the backward cleaning using the cleaning solution or the cleaning gas in order to remove the suspended matter stuck on the surface of the disc filter.
The sample, however, cannot be filtered during the backward cleaning. In a case where the sample includes a large amount of suspended matter, the backward cleaning needs to be carried out frequently, and therefore, it is impossible to continuously supply the filtrate to the analyzing apparatus.
A method of cleaning the disc filter, therefore, which is different from the backward cleaning has been proposed (see Japanese Unexamined Patent Publication No. 2009-142746). The proposed filtration apparatus includes a filtration device housing, inside itself, a cylindrical disc filter. A sample introducing port (sample inlet) for introducing a sample is formed at a lower portion of the filtration device, and a sample discharge port (drain outlet) is formed at an upper portion of the filtration device. Part of the sample introduced from the sample introducing port passes through a clearance in the disc filter. At this time, the suspended matter included in the sample adheres to a surface of the disc filter and the filtrate which has passed through the disc filter passes through an inner flow path in the disc filter, and is introduced to a filtrate discharge port. The rest of the sample introduced from the sample introducing port passes by the disc filter and is discharged from the sample discharge port. At this time, the suspended matter stuck on an outer surface of the disc filter is unstuck by the sample flowing by the disc filter and is discharged from the sample discharge port together with the sample. Therefore, it is possible to remove the suspended matter stuck on the outer surface of the disc filter without carrying out the backward cleaning for causing the cleaning solution or the cleaning gas to flow from the inside toward the outside of the disc filter.
Although the suspended matter stuck on the outer peripheral portion of the disc filter can be removed by the sample flowing by the filter in the above structure, the suspended matter stuck on the inner side cannot be removed. Therefore, it is impossible to completely prevent occurrence of clogging of the disc filter and the filtration apparatus needs to be disassembled for maintenance of the disc filter, or the backward cleaning needs to be carried out periodically.